The Sony Dash has no future. Once Sony turns off their servers you might be able to use it as a paperweight.
The Chumbys and Infocasts will keep going as long as you have working hardware. Even if the servers go dark at some point there is more than one way to continue their usefulness.
I have a Chumby One and an Infocast 8 (running Chumby 8 firmware). They are different devices and tend (for me) to fill different uses. While they are still available you might want to pick up a Chumby 8 or Infocast 8 to compliment your Chumby ones.
Tar, feathers, congress. Some assembly required.